Diodes and Applications: Topics, Subtopics, Study Flow, and Working Steps

The V-I curve shows how diode current changes with diode voltage. In forward bias, current remains small until the junction barrier is overcome, then it rises sharply. In reverse bias, current remains nearly zero except for a small leakage current until breakdown.

Static resistance is the large-signal ratio of diode voltage to diode current at a chosen operating point. It tells you the average opposition seen from the origin to that point on the V-I curve.

Dynamic resistance is the small-signal resistance around the operating point. It depends on the local slope of the V-I curve, so it becomes small when diode current is large.

A Zener diode is designed to operate safely in reverse breakdown. When reverse voltage reaches the Zener value, it holds nearly constant voltage while current changes within a safe range.

An LED converts carrier recombination energy into light. It must be forward biased, and current must be limited because after turn-on the diode current can rise quickly.

A photodiode converts light into current. It is commonly used in reverse bias so the depletion region is wide and light-generated carriers are swept quickly by the electric field.

A Schottky diode uses a metal-semiconductor junction. Because it mainly involves majority carriers, it switches fast and usually has a lower forward voltage drop than a normal silicon PN diode.

A varactor uses the depletion region as a voltage-controlled capacitor. Reverse bias changes depletion width, which changes capacitance.

A half-wave rectifier uses one diode so only one half-cycle reaches the load. The other half-cycle is blocked, which makes the circuit simple but ripple-heavy.

A full-wave rectifier uses both half-cycles of the AC input. The load current direction remains the same during positive and negative half-cycles, improving average output and reducing ripple compared with half-wave rectification.

A bridge rectifier uses four diodes to achieve full-wave rectification without needing a center-tapped transformer. In each half-cycle, two diodes conduct and two block.

A capacitor filter is connected across the load. It charges near the rectifier peak and discharges through the load between peaks, filling the gaps in the waveform.

An inductor filter is placed in series with the load. It opposes sudden current changes, so it tries to keep load current smoother.

An LC filter combines current smoothing from the inductor and voltage smoothing from the capacitor. The pair attenuates ripple more strongly than either element alone.

A Zener regulator uses reverse breakdown as a voltage reference. The series resistor absorbs extra input voltage and limits current, while the Zener holds the load voltage close to its breakdown voltage.